Obtaining azimuthal information has been an important aspect in well logging for many decades. Initially, wireline measurements, in particular of resistivity, were used to determine the dip of formations penetrated by a well bore with respect to the axis of the wellbore. These measurements were expanded and refined to obtain high resolution resistivity images.
The advent of logging while drilling (LWD) and measurement while drilling (MWD) tools, which are incorporated in the drill string and allow measurements during the drilling process opened new possibilities and brought new applications. The fact that the tool is rotating during the drilling process makes it possible to perform an azimuthal and axial scan during the drilling process, if the instrument has sufficient azimuthal and axial resolution.
In particular, obtaining azimuthal measurements and making images from nuclear logs became a possibility as indicated for example in U.S. Pat. Nos. 5,539,225, 6,944,548 and 7,073,378 assigned to Schlumberger regarding imaging using tools equipped with neutron sources. Images can also be obtained from tools using gamma ray sources or from tools that detect natural gamma rays.